glad to know it works for you now... I wasn't sure how the 2 spark plugs worked on these, I know Nissan used to use 2 plugs per cylinder one was intake and one was exhaust... the exhaust one fire just after the exhaust valve closed to help burn any excess fuel

To me what Lance said makes the most sense to me. One coil - two wires, spark would have to reach the plugs at the same time and that would be a little before TDC on the compression stroke. At less thatís what I'm thinking.

Slim or anybody else, just how does the two plugs per cylinder work? I thought they both fired at the same time, both for fuel. If one is for fuel and one for exhaust, which one is which. Does marbeling come into play here at all?

glad to know it works for you now... I wasn't sure how the 2 spark plugs worked on these, I know Nissan used to use 2 plugs per cylinder one was intake and one was exhaust... the exhaust one fire just before the exhaust valve opened to help burn any excess fuel

Jeez slim, I thought you were just "funnin'" him in the first post you made. I`ll be the first to admit that I don`t know a lot about Nissan or any other Japanese cars, but I have never heard of this second spark to burn the exhaust gases. I thought that the catalytic converter was supposed to take care of any unburned hydrocarbons in the exhaust system.

My understanding of having two spark plugs per cylinder, is that they both fire at the same time to get a more complete burn of the fuel, and more power and efficiency.

Do you know of a link anywhere that discusses this process that Nissan used or uses? It sounds "off" to me.

Jeez slim, I thought you were just "funnin'" him in the first post you made. I`ll be the first to admit that I don`t know a lot about Nissan or any other Japanese cars, but I have never heard of this second spark to burn the exhaust gases. I thought that the catalytic converter was supposed to take care of any unburned hydrocarbons in the exhaust system.

My understanding of having two spark plugs per cylinder, is that they both fire at the same time to get a more complete burn of the fuel, and more power and efficiency.

Do you know of a link anywhere that discusses this process that Nissan used or uses? It sounds "off" to me.
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Not sure where to look for info that supports my claims other than NAPA... look up a 1986 Nissan Pickup with the 4 cylinder engine. there will be 2 spark plug numbers, one is for intake and one is labeled exhaust. I used to ask how this worked as well, because I too thought that the two spark plugs would fire at the same time, to cause a ore efficient burn, and the catalytic converter would do the rest. The afterburn spark theory is that they could reduce eissions even further if the raw unused gas was burned before the cat.
Now on our bikes I have no clue why they have 4 plugs... it seams to me that two would be just fine.

I am going to do a little bit ore research into this on the bikes, because I never heard of running 2 sparkplugs per cylinder for combustion burn. I'll report y findings back here:

UPDATE: Ford used the dual spark in the mid 90's Rangers... the Ranger's system fires both intake and exhaust at the same time to achieve ah otter burn, and supposedly higher engine revs. Nissan used there system like I mentioned above. I also found more but its going to take e a while to sift through it all and make scene of it

Last edited by slimvulcanrider; 08-22-2009 at 10:58 AM.
Reason: added more info

What if, a person was to take a run and note how it ran and sounded. Then did the same run again, only pull both left side plug wires off and see if there was a difference. Then do the same thing with the right side. You might only get to the end of the driveway and know. I've seen cutaways of a car motors showing the cycle of the vales and plug firing. Anyone seen one for the vn750? That might tell the story.

What if, a person was to take a run and note how it ran and sounded. Then did the same run again, only pull both left side plug wires off and see if there was a difference. Then do the same thing with the right side. You might only get to the end of the driveway and know. I've seen cutaways of a car motors showing the cycle of the vales and plug firing. Anyone seen one for the vn750? That might tell the story.

I was looking for just that same info myself. Your proposed ride sounds good though...

That might be an interesting test. Only remember to ground the pulled plug wires by some means or the bike won't run at all.

I believe that starting the flame front at two points gives faster burning as the flame front area then grows faster at the beginning of the combustion. At least that is my common sense deduction. That should be a good thing at higher revs.

Ford and Nissan did make a 4 cylinder with 2 plugs per cylinder. The plug wires for the same cylinder came from different coil packs on the Ford and and eight plug distributer cap was used on the older Nissan. On the Ford the first plug fired around 10 degrees BTDC the second one fired a few degrees ATDC on the power stroke. It was nicknamed the "suck me blow me" Head.

The reason our bikes have two plugs plugs is so the air /fuel mixture can burn twice as fast and more completely than with one plug. With one plug the the burn starts at the plug side then has to travel to the other side. With two plugs the burn starts at both plugs equaly and burns to the center in half the time of one plug.

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